Bluetooth physical link type: SCO and ACL link

The Bluetooth physical link ACL (asynchronous connectionless), the other link is the SCO (synchronous Connection oriented) is mainly used to transmit time-demanding data communication.
Bluetooth baseband technology supports two types of connections: synchronous directed connection (SCO) type and asynchronous no connection (ACL) type. The former is mainly used for synchronous voice transmission, the latter is mainly used for packet data transmission.
The SCO connection is a symmetric connection that transmits packets using the reserved timeslot. After the connection is established, the master device and slave device can send SCO packets without being selected. SCO packets can either transmit voice or transmit data, but only use it to re-send the damaged portion of data when transmitting data. The synchronous directed link (SCO) is a point-to link between the main unit and the slave unit in the Pico network. The main unit maintains SCO links through regular use of a reserved timeslot.

An ACL link is a directed sending packet that supports both symmetric and asymmetric connections (either one-to-one or one-to-many). The master device is responsible for controlling the link bandwidth and determining how much bandwidth and connection symmetry each slave device can occupy in a Pico network. Data can be transferred only when the device is selected. The ACL link also supports receiving broadcast messages from the primary device to all slave devices in the Pico network. An ACL link is a point-and-click connection between the main unit and all the slave units in the Pico network. In this connection mode, the main unit does not retain the SCO link with a timeslot, and the main unit establishes an ACL link to any other slave unit on each timeslot base. This includes the slave units that have been scheduled for use in SCO link mode.

Bluetooth Baseband grouping format:

From: http://blog.chinaunix.net/uid-23193900-id-3272169.html